Sulfones are available for a wide variety of purposes and may be used in the manufacture of plastics in fabric finishing, as additives to textile fibers, as dyestuffs or adjuvants to dyestuffs and as therapeutic compounds in processes and treatments well known in the art.
Conventionally, sulfones may be made by several different techniques and generally it is possible to react an organic compound R--X with sodium sulfide to yield the organic sulfide R--S--R in accordance with the formula EQU 2R--X + Na.sub.2 S .fwdarw. R--S--R + 2 NaX
where X is a halogen atom, S is sulfur and R is the organic radical. The sulfide R--S--R is oxidized in a second stage to the sulfone with an oxidizing medium such as potassium permanganate or nitric acid or by catalytic systems. The oxidation may be represented by the simplified formula EQU R--S--R + O.sub.2 .fwdarw. R--SO.sub.2 --R
where the reaction product R--SO.sub.2 .sup.---R is the sulfone. In accordance with the present invention, a process for the production of sulfones utilizes the fact that the SO.sub.2 .sup.- ion can replace certain functional groups of an organic compound in an organic medium (nonaqueous solvent) in which the SO.sub.2 .sup.- ion is formed by electrolysis.
The atoms or groups of a number of organic compounds have been found to be replaceable by SO.sub.2 .sup.- formed by electrolytic dissociation in an organic medium.
The present invention thus involves the steps of electrolyzing an organic medium containing sulfur dioxide (SO.sub.2) to produce SO.sub.2 .sup.- ions in the presence of an organic compound R-X (or a group of such compounds) where R is an organic radical and X is an atom or group of atoms replaceable by SO.sub.2 .sup.-, thereby resulting, after some secondary reactions, in R--SO.sub.2 --R.
The reaction is carried out in an aprotic organic solvent (nonaqueous medium) containing a salt, preferably a quaternary ammonium salt, designed to provide the necessary conductivity for the electrolysis current which transforms the SO.sub.2 .sup.- into SO.sub.2 .sup.-. Preferably the salt is a tetra-alkyl ammonium salt such as tetramethyl or tetraethyl ammonium chloride or bromide.
The compounds R-X which are used in accordance with the present invention are preferably the organic halogen compounds, the sulfonic-acid esters and the sulfuric-acid esters although any compound capable of replacement of the group X by SO.sub.2 .sup.- may be employed.
According to the present invention, the organic compound is introduced into the medium or constitutes the reaction vehicle in which the sulfur dioxide is dissolved and the system is then subjected to electrolysis. Of course, a system in which the organic compound is in liquid form and can constitute the reaction medium or vehicle as well as one of the reactants, has the advantage that recovery of the sulfone is simplified. Organic compounds which can operate in this manner are dimethylsulfate, chloroacetonitrile and chloroacetone. The latter compounds require no separate solvent.
It has been found to be advantageous to prevent the electrolysis current from exceeding the maximum usable current density that produces only the SO.sub.2 .sup.- -ions. This can be accomplished by providing in the electrolysis cell a reference electrode which is not traversed by the electrolysis current and controlling the voltage between the reference electrode and the cathode so that with respect to the standard potential of the sulfur dioxide/sulfur dioxide anion REDOX couple (SO.sub.2 /SO.sub.2 .sup.-), the potential does not exceed 0.1 volt. It has been found that best results are obtained when the sulfur dioxide concentration in the solution during electrolysis is at least 0.1 mole/liter.
The process of the present invention also has the significant advantage that it is possible to produce polymeric sulfones readily. It is only necessary, to this end, to use an organic compound having more than one halogen atom, i.e. a compound of the type X--R--X where R is a difunctional organic radical and X is an atom or group replaceable by SO.sub.2 .sup.-. The reaction follows the overall formula EQU 2n (X--R--X) + 2n(SO.sub.2) + 4ne.sup.-.fwdarw.-R--SO.sub.2 --R--SO.sub.2 + 4n X.sup.-
where n is an integer, e.sup.- is the electronic charge, R and X have their earlier-stated meanings and --R--SO.sub.2 --R--SO.sub.2 --is the repeating group of the polymer.
Of course, cyclic sulfones can also be produced from organic compounds having terminal X groups the C atoms to which they are attached being bridged by the --SO.sub.2 -- group.
It has been found to be most advantageous to carry out the reaction in an electrolysis cell subdivided by a diaphragm or ion-exchange membrane into a cathode compartment and an anode compartment. When an anion ion-exchange membrane is used, the current through the cell is brought about solely by migration of the anions X.sup.- liberated by the cathodic process. The anions traverse the membrane and are oxidized at the anode. When X is a halogen atom, preferably chlorine or bromine, the halogen X.sub.2 is liberated at the anode as the free halogen. The sulfone is formed in the cathode compartment. The system has been found to reduce side reactions which might tend to form impurities. A cell of the character described has been found to have an especially high yield of sulfones.
In the process of the present invention, the sulfones or sulfone mixtures can be separated from the solvent by distillation or by extraction with the extraction effluent then being distilled. For the extraction solvent, it is preferred to use a compound in which the salts (provided for conductivity) are insoluble. Such a solvent may be chloroform. The salt recovered in this manner may be recycled to the cell and even the free halogen may be used in ancillary chemical reactions.